Noise induced hearing loss (NIHL) is the most common occupational disease. Typical industrial workplace has a complex noise environment, in which impulsive noises occur with a continuous background noise. Current noise guidelines integrate impulsive and continuous noises by the equal energy hypothesis (EEH), which is an approach widely considered invalid for impulsive/complex noise environments. This project aims to develop a quantitative procedure to assess the risk of exposure to complex/impulsive noise environments based on a solid theoretical and experimental foundation. Three specific aims to be pursued in this research are; (Aim 1) Develop a tool for time-frequency domain noise characterization: An advanced time-frequency (T-F) noise characterization tool will be developed by refining and extending the modified analytic wavelet transform (AWT) method proposed by the PI. The characterization tool will be applied to the complex noises used in chinchilla based NIHL studies conducted by the consultants of this project and correlations between the noise characteristics and hearing losses will be studied. (Aim2) Develop a quantitative procedure for NIHL risk assessment: Several noise metrics will be formulated as functions of T-F characteristics of noise. Their correlations with hearing losses observed in chinchillas will be compared, which will identify the metric that best represents the hazard of complex noise. Employing this metric, a general noise hazard assessment procedure will be developed, which will consist of measurement, signal analysis and risk evaluation parts. (Aim 3) Design future NIHL study and test protocol: Based on the experience of developing the new noise hazard assessment method, studies that become necessary or possible because of the capability of the new T-F noise characterization tool will be identified, which will then be combined to develop a protocol for future research. [unreadable] [unreadable] [unreadable]